Liquid-solid phase equilibria in metal-rich Hf-Ti-Si alloys

A range of metal-rich Hf-Ti-Si alloys with Si concentrations up to 35.0 at.% was directionally solidified. Liquid-solid phase equilibria in these alloys have been investigated using scanning electron microscopy, X-ray diffraction, and electron beam microprobe analysis. Four phases were identified: (Hf,Ti) ₅Si₃, Hf(Ti)₂Si, β(Hf, Ti, Si), and α(Hf, Ti, Si). Microstructural and microchemical evidence provided a clear definition of the Hf-Ti-Si liquidus surface at the metal-rich end and indicated the existence of the invariant reaction: Liquid + Hf(Ti)₂Si → (Hf, Ti)₅Si₃ + β(Hf, Ti, Si) This invariant reaction occurs at a composition of approximately Ti-50Hf-9.5Si, and at a temperature of ∼ 1420°C.